The present disclosure relates to radio frequency devices, and more specifically, to apparatus and methods for isolating transmission lines in radio frequency (RF) devices.
Radio frequency devices may include one or more transmission lines arranged on a substrate that are operative to propagate RF signals. The RF signals may cause interference in the devices if the transmission lines are not properly isolated from other transmission lines, integrated circuitry, or other features arranged on the substrate.
FIG. 1 illustrates top view partially cut-away view of a prior art example of a portion of an RF device arranged on a substrate 100. The illustrated example includes transmission lines 102 arranged on the substrate 100. The transmission lines 102 include a conductive material, and are operative to transmit RF signals as indicated by the arrows 101. A plurality of conductive vias 104 that are connected to ground is arranged between the transmission lines 102. The conductive vias 104 are sized and spaced such that RF signals in a particular range of frequencies do not pass through the arrangement of conductive vias 104. The spatial distance (a) between the conductive vias 104 is partially dependent on the frequency of the propagated RF signals. In this regard, a device designed to propagate a higher frequency RF signal would have more conductive vias 104 spaced at a smaller distance than a device designed to propagate a relatively lower frequency RF signal.
FIG. 2 illustrates a side cut-away view of the prior art example along the line 2 of FIG. 1. Referring to FIG. 2, the transmission lines 102 are disposed on the substrate 100 that include a dielectric material. The transmission lines 102 are capped with a capping layer 202 that includes an insulator material. A first conductive layer 204 is arranged on the capping layer 202 and a second conductive layer 206 is arranged on an opposing surface of the substrate 100. The conductive via 104 is communicative through the substrate 100 and the capping layer and is electrically connected to the first conductive layer 204 and the second conductive layer 206. The first conductive layer 204 and the second conductive layer 206 are connected to ground such that the conductive vias 104 are grounded.